Apparatus for reproducing images in color



March 6, 1954 P, H. WERENFELS APPARATUS FOR REPRODUCING IMAGES IN COLOR6 Sheets-Sheet 1 Filed Oct. 11 1951 INVENTQR .Rier erarg eh Q ATTORNEYMarch 16, 1954 p H, WERENFELS 2,672,575

APPARATUS FOR REPRODUCING IMAGES IN COLOR Filed Oct. 11, 1951 3Sheets-Sheet 2 March 16, 1954 P. H. WERENFELS APPARATUS FOR REPRODUCINGIMAGES IN COLOR Fil ed Oct. 11 1951 S Sheets-Sheet I5 INVENTOR fsllgrelf/yelp ORNEY ing directions. phosphors are activated in a given orderas the Patented Mar. 16, 1954 APPARATUS FOR REPRODUCING IIWAGES IN COLORPeter H. Werenfels, Lawrenceville, N. J assignor to Radio Corporation ofAmerica, a corporation of Delaware Application October 11, 1951, SerialNo. 250,867

3 Claims.

1 This invention relates to improved cathode ray tube apparatus forreproducing images in color.

Color kinescopes have been constructed employing directional colorscreens that emit light of one primary color or another depending onmounted with the perpendicular bisector of one particular side of theequilateral triangle pointing in opposite directions that areperpendicular to the row. Thus one side of alternate triangles isparallel to the upper edge of a row and the corresponding side ofintermediate triangles is parallel to the bottom side of a row. Thephosphors may be spots on a plane surface, they may be coated onto threesides of a solid such as a.

pyramid, or, they may be coated on the insides of a hollow hexahedron,etc. The important factor is that the different color responsivephosphors must be arranged so that they can be scanned in one order by abeam tracing a closed nonintersecting path in one direction and in a'reverse order when the beam traces a different closed path but in thesame direction. A target formed in this manner Willbe referred to as adirectional target. I

The directional target is activated by-a single beam that is rotatedabout its normal path so as to approach the screen from cyclicallychang- The difierent color emissive .in the name of Sziklai, Schroederand Bedford,

improved results canbe obtained if "the transmitted signal representsthe primary colors in one sequence during one interval of time and areverse sequence during another interval.

It is the principal object of this invention to provide a new andimproved way of reversing the sequence in which the different primarycolors are emitted by color kinescopes of the type described above.

Briefly this objective may be attained by shifting the centering of thebeam or beams of electrons before they are focussed so that a differentgroup of phosphors is scanned. In addition, for reasons that will betreated in detail below, the phase of the rotation of the beam about itsnormal path must be altered when the centering is changed.

The manner in which this objective maybe reached will be betterunderstood from the detailed description of the drawings in which:

Figures 1 and 1A show the details of a single beam color kinescope thatmay be employed in the combination of the present invention.

Figure 2 is a view of the phosphor dot screen as it is seen through themask of the color kinescope of Figure 1,

Figure 3 is a view of certain of the apparatus in Figure 1 useful inexplaining the operation of the present invention. 1

Figure 4 illustrates a circuit that may be employed to change thecentering of the beam on successive fields. a

Figure 5 is an enlarged view of the phosphor spots employed in one typeof directional screen and Figure 6 illustrates a type of coincidencecircuit that may be employed.

Referring to the drawings, Figure 1 shows one form of single beam colorkinescope that may be used in the present invention. The tube consistsof an evacuated envelope l0, having both a conical portion l2 anda'tubular neck portion Id coaxially joined together as shown. Theconical portion l2 of the envelope is closed by'a'face plate I5 andclosely spacedfrom it is a fluorescent target and screen structure l8 tobe described below. Mounted coaxially within the tubular envelope [4 isan electron gun structure for projecting a beam of electrons 20 towardthe screen structure'l8. The electron gun is of conventional design andconsists of a cathode cylinder 22. i

A control grid cylinder 24 coaxiallysurrounds the electron emitting endof the cathode 22 and has an apertured plate structure closing one endthereof and closely spaced from the cathode. A shield electrode or grid26' constitutes a short thimble-like electrode having an aperture in thebottom thereof for the passage of electrons therethrough. Spaced alongthe tubular neck portion Hi and coaxial with the other electron gunparts is a tubular first anode electrode 28, having an enlarged portionat the end facing the fluorescent screen I 8.- A- second anode electrodeis formed by a conductive coating 30 on the inner of a converging natureand cause the electrons to form into a beam having a minimum crosssection or cross-over point 56,be tw een the tubular electrode 28 andthe screen It. beam, after passing through this cross-over point 56,tends to diverge before striking the screen H3. The diverged beam isbent away from the central axis of the tube by a rotating radialmagnetic field. As is well known in the art, such a izleld canbegenerated by applyingcurrent of one phase to afi-rst pair of coilsthat are diametrically. mounted about the neck of the .tubaand applyingcurrent of a different phase to a second pairof coilsthat are mountedwith their axis at 9Q?-to, the first pair. For simplicity, the coils areshown as one yoke 3|. The focusing coil 3% serves to-converge theelectrons within the beam and also .to direct the beam to the same pointin the region of thetarget 18. shown, this pointis the. same point on amask 44; that the beam would havestruck. if the coils were not used.Thus, the beam substantially generates a cone.of revolutionhaving anapex at thelmask .44.-

The electron beam 20 andhencethe apexot the cone, of revolution maybecaused to scan over thesurface of themask 44 in any desired pattern orraster.

from topto the-bottom of the screen. [8. The scanning of the beam isproduced by. scanning fieldsestabIishedby twopairs of scanning coilsincluded in the yoke .40. Each pairof coils may be connected to wellknown circuits producing saw-tooth currents forv providing both line andframe scansion of the beam.

In the screen structure l8 the masking electrode 44=is positioned infront of atransparent phosphor supporting sheet 45. electrode 44 isformed: from thin metallic foil which is opaque tothe electronsof thebeam 20. A plurality of apertures 48 are formed through the metal foilof the masking electrode 44. Supported onthe surface of the transparentplate,

46 are areas 50 of phosphor coating which are positioned in the path ofthe beam 20 passing through apertures 48.

In the enlarged section of the screen 18 shown in Figure 1A it can beseen that if the electron b'amapproaches the target from any one of thedirections indicated as X, Y or Z, the electrons oflthebeam will passthrough the-apertures of themasking electrode 44 and strike thosephosphor spots which arein line with the beam path.

coincident with these directions. When the beamapproaches the targetalong a path X it strikes only those phosphor coatedspots indicated byR, which luminesce with a red light.

In a similar manner, when the beam approaches.

The electron In the embodiment.

However, in tubes of this type, the 7 conventional scanningconsistsofparallel lines,

The masking,

10 2 spots in sequence.

circle with its center at a point l3. If the ouring the target along apath Z will strike those phosphor areas indicated by the letter B, whichluminesce with a blue light.

'1 hus, the combined efi'ects of the rotating field oi coils and that ofthe focusing coil 34 result in beam is being first displaced from itsnormal path and then redirected alonga new path to strike the. surfaceoftarget lcfrom sequentially different directions so as to strike thephosphor The cross sectional area of the beam at the mask 44 may belarge enough to cover a plurality of the apertures 48. Electrons passthrough each of theapertures covered by the beam to form a; sectionalbeams having a direction depending on the rotational angle of the mainbeam about its normal path. As the main beam rotates, the sectionalbeams also rotate and scan circular paths on the screen i8 havingcenters 10. In Figure 2 certain groups of phosphor dots 10 are soarranged that their geometriccenters. coincide with thecenteixof thecircular-path traced on the screen I8 by thesectional beams. Assumingfor the moment that the beam .20 is not scanning a raster, but isrotating aboutits normal position in a clockwise direction, it can be-seen from an examination of Figure 2 thatthe sectional beams i0will-scan aroundithe red; blue, and green phosphor spots of the groups!the order named; Nowif the centersof the substantially circular pathstracedby thelsectional beams are shifted to the corresponding points E2,the beam scans.red,.green, and blue phosphor spotsin the order named.This-order of scanning the spots isjust=the reverse of the ordercentering is as it passes throughthe beam rotation coils. Whether themeansemployed is electrostatic or electromagnetic the shiftshould be ina direction that is the opposite from the direction to 12; that is fromT2 to 10. The

"reason for this will become clear from the following discussion of theelectron optics of thetube of Figure 1. essential components of theelectron-optic system are illustrated in Figure 3. The electron gunshown in Figure 1 directs a beamof electrons along the principal. axisof the tube-to a point 0 that is centrally located with respect to therotating magnetic field-set up by the beam rotation coils. In normaloperation, the beam 20is bent away from the principal axis of the tubeand rotatdi The paths 27 my and g indicate different positions the beam20 may assume as the radial magneticfield established by the coilsrotates. The loci of the beam in the plane of thefocusing coil 34 is arent in the focusing coils is properly adjusted, the origin""0 of thebeam is imaged atthe point i."-" I'his"latter poinft is at the,apertures of the mask and iseffectively the focal or cross-over point.With nopurrent flowing in the deflection coils 40; thebea-m wouldgenerate a cone of revolution having its apex at the point 2'. Now ifthe beam is deflected, the apex scans to a point It should be noted thatthe focusing coils serve to'focus at'th'e point i or 2" as the case maybe, j both the electrons within the beam and the beam itself, regardlessof its position in the loci.

In one embodiment of this invention, the beam is shifted from the pointI) to the point as it "passes" through the beam rotation coils.

Thus the loci of the beam in the plane of the focusing coil 34 isindicated by the dotted circle I having a center 16.

As is well known to those Skilled in the art, this change in the angleof If the rows of phosphor spots The of the beam and perpendicular tothe direction 0, 0. The shift in centering might also be efiected byelectrostatic plates that set up an electrostatic field along the line0, 0'. Normal centering of the beam and hence theraster 'on the tube maybe effected by controlling the amount of steady current flowing in thedeflection coils 40. Thus normal centering acts the same as a steadyamount of deflection, and the center of deflection is still the same asillustrated by the deflected beam in Figure 3 that strikes the screen at2'. When the normal centering control is adjusted, the beam still landsat the same place with respect to the phosphor groups. displace theelectron paths toward the focusing field, however, the electronsapproach the screen from a different direction and land at a differentplace on the screen I8 with respect to the phosphor groups. The shiftingof the centering could take place at other points than the axialposition of the beam rotation coils but must take place before thefocusing field is reached.

This shift in the beam in one direction, up-

ward and to the right as shown in Figure 3, ac- 'tually displaces thescanned raster and hence signals representing a certain point in thescene being reproduced are reproduced at two different positions as thebeam is shifted to effect a reverse sequence of color reproduction. This'misregistration is negligible if the groups of phosphors are small incomparison with the maximum amount of detail to be reproduced. If thegroups are relatively large, the horizontal displacement can becorrected by changing the phase of the incoming video signals that are"used to modulate the intensity of the beam or beams with respect to thescanning action of the beam.

Figure 4 illustrates the manner in which the centering of the beam ofthe tube shown in Figure 1 may be shifted on successive fields. Thetransmitted signal is detected on a standard receiver 90 and applied tothe grid of the color tube and to the deflection circuit 92 in thenormal manner. The signals are also applied to a color synchronizingcircuit 94 such as described in RCA Bulletins on Color Television andUHF October 1949. A sampling oscillator 96 is controlled by thesynchronizing circuit 94 and provides the energy that is to be appliedto the beam rotation coils. The sampling frequency applied by theoscillator 96 is applied to the grid of an amplifier 98 via a delay lineI00 and to the grid of an amplifier I02 directly. The plates of theampli- If the change in centering is such as to a beam rotation coil 60.Thus if the amplifier 98 is conducting, the sampling frequency isapplied to the beam rotation coil 60 with a delay determined by thedelay line I00 and if the amplifier is cut off and amplifier I02 isconducting, the sampling frequency is applied directly to the beamrotation coil 60 without any delay. The reasons for this delay will bediscussed more fully in connection with Figure 5.

In order to shift the beam as previously discussed, the presentapparatus supplies current to the centering coil 19 during one field anda different amount of current to this coil during a succeeding field. Inorder to effect th'isresult, the horizontal and vertical sweep signalssupplied by the deflection circuit 92 are applied to a coincidencecircuit I06 which is described in detail in connection with Figure 6.The coincidence circuit provides a pulse at the beginning of every otherfield. These pulses are applied to trigger a multivibrator I 08. Themultivibrator I08 may be a free running type having a cycle equal to twofields or it may be a monostable multivibrator that is triggered to anunstable state by the coincidence pulse, reverting to its stable stateat the end of a field. In either case, the multivibrator l08 willprovide, as is well known to those skilled in the art, oppositely phasedrectangular waves as illustrated by the wave forms H0 and H2; These waveforms are applied to the grids of the amplifiers 98'and I02 respectivelyso that one is conducting while the other is non-conducting and viceversa. Thus during one field the sampling frequency supplied by theoscillator 98 is applied to the beam rotation coils 50 via the amplifier98 and the delay line I00, and in the next field it is applied directlyto the beam rotation coil 60.

One output of the multivibrator I08 is applied to an amplifier H4, theplate of which is connected to 18+ via the beam centering coil I9. Hencewhen the amplifier H4 is rendered conductive by the positive portion ofthe wave form H2 a large amount of current fiows through the centeringcoil 19. When the amplifier H4 is cut off during a negative portion ofthe'wave form H2 the amount of current flowing through the beamcentering coil 79 may be substantially zero. The amount of currentfio'wing through the beam centering coil 19 when the amplifier l M isconductive may be adiusted by rheostat H6 that is connected in parallelwith the beam centering coil I9. When the amplifier I I4 isnon-conductive, the amount of current flowing through the beam centeringcoil I9 can be controlled by a rheostat H8 that is connected be tween.the plate of the amplifier l I4 and ground.

The overall operation of the apparatus in Figure 4 is as follows. Duringone field the amplifier 98 may be cut off and the sampling frequencyfrom the oscillator '96 is applied directly to the beam rotation coils60. At the same time,

the amplifier H4 is rendered conductive and current flows through thebeam centering coil 79 so as to shift the beam from the points I0 on thephosphor screen of Figure 2 to the points '12. During the next field,however, the amplifier 90 is rendered conductive and the amplifier I02is cut off, with the result that the sampling beam, strikes the,phosphorscreen vof Figure) at points 10.-

The following. discussion .relates to the reasons for the use of thedelay linev I in the apparatusof Figure 4. Figure shows .an enlargedView of some of the phosphor spots. When thelocus traced by the rotatingbeam is centered at the points '52, and assuming that the beam rotationis in. a clockwise direction, the order of color reproduction is red,green, blue,v red, etc. When the beam is shifted so that the center of[its locus is at the points 10,- the same direction of rotation willscan the red, blue, green, red spots in sequence. This sequence, aspreviously noted, is the reverse of the sequence when it follows a pathcentered at [2. Assume that thebeam is centered atthe point 12 and thatthe resultant magnetic field is such that the beam strikes a redphosphor spot I20. If the beam. is now shifted by the action of the beamcentering coil i9 soas to follow a circular path having H! for acententhe beam strikes a point midway between the red phosphor spot H29and abluephosphor spot !22. However, at this time the signal transmittedrepresentsred and not a combination of red and blue. Therefore, in orderto insure thatthebeam lands on the red spot, the phase of the beamrotation must be retarded by 6O". The delay line Hi0 must thereforeintroduce a delay of one-sixth of a cycle of the sampling frequencysupplied by the oscillator 96;

Figure 6 illustrates one form-that the coincidence circuit H35. ofFigureb mayv assume. A multi-grid tube I is biased to cut off by placinga positive potential on its cathode as shown. The horizontal flybackpulses are applied to .a grid 12! by an ordinary RC coupling network.The

vertical fiyback pulses are differentiated by an RC coupling network 128before being applied to a grid I29. When the two feedback pulses occursimultaneously, as is the case on every other field, the cut off bias onthe cathode of c the tube 25 is overcome and a pulse appears at itsplate. It is this pulse that triggers the multivibrator H18.

In the embodiment of the invention discussed above, the beam wouldnominally strikethe screen iii-at the points 10. The order of scanning.the spots was reversed by shifting the beam so that it would normallystrike the screen. 18 ofv the points 12. Little or no current wouldthenbe passed through the beam shiftingcoil- Hl'when the path. of thebeam was to be centered-at the points E9 and a predetermined-amount ofcurrent would be in the coil 19 when the beam is to be shifted so as totrace paths centered at points '12. The beam might normally be centeredat any point on a line between the points Til-and E0 in which case thecurrent through the coil 19 would flow in one direction when the path ofthe beam on the screen I8 is to be at points 12 and in the oppositedirection when the path of thebeam is to be centered at points 10. Ifthe beam would normally land at points on the screen 18 that are notalong a line 12-10, then two sets of beam shifting coils providingintersecting fields would have to be used. Current through one of themwould center the path traced by the beam at points 72 and currentthrough the other would center the path traced by the beam on the screenl8 .at points 10.

Thebeam could also be shifted downward so of Figure 4 by one half cycleof the beam rotationalfrequency.

It is not necessary that the center of the path tracedbythe beam or thescreen 18 be shifted to thenearest group of phosphors that providesreversal of the primary colorreproduction. The shift can skip any numberof groups as long as the groups traced afterthe shiftarle such thatrotation about them in same direction produces a reversal inthe sequencewith which the phosphors of the diiferent primary colors are scanned.

The apertures 48 in the mask 44 could also be oriented differently withrespect to the phosphor groups without interfering with the presentinvention.

Having thus described the invention whatis claimed is:

1. Cathoderaytube apparatus comprisingin combination a directionaltarget having diiferent colorphosphors mounted in groups along each lineof the raster, an electron gun adapted to direct a beam of electronstoward said target along a given path, means for bending said. electronsaway from said path, the plane in which said bending occurs beingrotated, means for focusing said beam in the region of said target,-means for deflecting said beamso that it scans a raster at said target,means located between. said gun and said focusing means for directingthe electrons along a given path during, a first interval and fordirecting said electrons along a diiferentpath. during a second intervalwhereby said rotating beam scans the difierent color phosphors on saiddirectional target in one sequence during the first interval and in,reverse sequence during the second interval.

2. Apparatus for reproducing images in color in response to signals thatare derived by sampling at a rate greater than line frequency theprimary colors of ascene in one order for a first interval of time andin a reverse order during a second interval of time comprising incombination a cathode ray tube, ,a directional color screen mounted insaid tube, an electron gun adapted to direct a beam of electrons towardsaid screen along .a given path,,means for bending said beam away-fromsaid path, the .plane of said bending beingrotated, means for focusingsaid'beam at a. point in the region of .said screen, means for laterallyshifting said beam before it passes through said focusing means, meansfor causing said beam to scana raster on said screen,.means forcontrolling-said beam shifting means so that the beam follows one pathduring said first interval and a different path during said secondinterval, and means for changing the phase of said rotating plane duringsaid second interval.

3. Apparatus for reproducing images in color from color signals that arederived by sampling each of a plurality of primarycolors from a scene inone sequence for a first interval of time and in reverse sequencelfor a.second interval of time comprising in combination a target comprise-:1of a phosphor dot screen, an apertured mask mounted infront of saidscreen, an electron gun adapted to project a beam of electrons towardsaid screen, means for establishing a rotating radial magnetic fieldthat is perpendicular .to said beam, a foc using. coiladapted toconverge said 2,672,575 9 10 electrons at the apertures in said mask,said ing the magnitude of said transverse magnetic focusing coil beingmounted so as to act on said field different during only one of saidintervals. electrons after they have passed through said ro- PETER H.WERENFELS.

tating magnetic field, a deflection yoke adapted to cause said focussedelectrons to scan a raster 5 References Cited 1n the file of this Patentat said target, means for establishing a trans- UNITED STATES PATENTSverse magnetic field that is at right angles to said beam, said lattermeans being mounted so as to 7 D i g A 1951 shift said beam at a pointbefore it enters the in- 2 Q 1952 fiuence of said focusing field, andmeans for mak- 10 I Fnen e a e a

